Presently, in investigating rock samples, electromagnetic (EM) evaluation methods exploit the response of an apparatus either to a single frequency or to multiple frequencies that are essentially governed by the same physics. Most EM formation evaluation is carried out by resistivity logging tools that are based on induction or galvanic principles. Multi-frequency measurements employed by resistivity tools are primarily used to optimize the measurement sensitivity for various formation and borehole properties, but do not provide substantially different information in terms of formation EM properties.
More recently, use of EM formation dispersion properties in the microwave frequency range has been proposed to obtain new petrophysical information. See, e.g., U.S. Pat. No. 7,376,514 to Habashy et al., U.S. Pat. No. 7,363,160 to Seleznev et al., and Freed, D., et al., “A Physics-Based Model for the Dielectric Response of Shaly Sands,” Trans. of SPWLA Annual Symposium, Jun. 25-29, 2016, which are all hereby incorporated by reference herein in their entireties.
EM formation evaluation has also been proposed in the low-frequency range of the EM spectrum (from a fraction of 1 Hz to hundreds of kiloHertz). See, U.S. Pat. No. 7,863,901 to Seleznev et al. In this frequency range, the formation response is governed by the physical phenomena collectively referred to as the “induced polarization effects”. See, Schlumberger, C., “Etude Sur la Prospection Electrique du Sous-Sol”, Paris Gauthier-Villars et Cie., 1920.